Photosoluble silver halide emulsion made spontaneously developable with amine boranes



United States Patent 3,451,819 PHOTOSOLUBLE SILVER HALIDE EMULSION MADE SPONTANEOUSLY DEVELOPABLE WITH AMINE BORANES Eugene Frederick Haugh, Old Bridge, N.J., assignor to E. I. du Pont de Nemonrs and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed Aug. 9, 1965, Ser. No. 478,421

Int. Cl. G03c 1/06 U.S. CI. 96-95 10 Claims ABSTRACT OF THE DISCLOSURE A photosoluble emulsion layer comprising before imagewise exposure to actinic radiation, a dispersion of light-sensitive silver halide crystals having intimately associated therewith a silver salt of an organic compound of lower solubility in water than silver chloride, said associated silver halide crystals dissolving more slowly in 10% aqueous sodium thiosulfate than untreated silver halide crystals at a predetermined pH; characterized in that the silver halide crystals are made spontaneously developable in ordinary photographic silver halide developing solution by treatment with at least one amine borane compound. A silver halide positive image can be intensified to a metallic silver image easily and conveniently.

This invention relates to photography and more particularly to improved image-yielding photographic silver halide emulsion layers and to improved elements embodying such layers. The invention further relates to processes for making and utilizing the novel elements.

In Blake, U.S. Patent 3,155,507, issued Nov. 3, 1964, there are disclosed photosoluble photographic elements containing silver halide crystals previously made to have a lowered rate of solution in a silver halide solvent by treatment with an organic compound capable of forming a silver salt of lower solubility in water than silver chloride. Such elements are capable of yielding a positive photographic image of silver halide by exposing imagewise to actinic radiation and then treating in a solution of a silver halide solvent which removes silver halide more rapidly in the exposed than in the unexposed areas. This positive silver halide image subsequently can be intensified by various means, e.g., by reducing the silver halide image to a metallic silver image. Ordinary photographic developing solutions can be used for intensification but the silver halide image must be fogged by light to ensure reduction to silver. In assignees copending application of Blake, Ser. No. 377,122, filed June 22, 1964, it was disclosed that these photosoluble elements could be improved by a prefogging treatment, using either chemicals or radiation, so that a positive, silver halide image formed therein could be intensified to a metallic silver image by a simpler and more convenient process. This treatment also extends spectral sensitivity.

It is an object of the present invention to provide improved photosoluble elements. More particularly, it is an object to provide such elements in which a positive silver halide image may be formed and then intensified by a simpler and more convenient process without a fogging step during the photographic processing. It is "Ice a further object to provide such elements having improved reproducibility. It is also an object to provide elements having extended spectral sensitivity, e.g., elements which may be exposed by light of the long.wavelength region of the visible spectrum. Still other objects will be apparent from the following description of the invention.

The above objects are attained in a photosoluble emulsion layer, comprising, before an imagewise exposure to actinic radiation, light-sensitive silver halide crystals having intimately associated therewith a silver salt of an organic compound of lower solubility in water than silver chloride, said silver halide crystals dissolving more slowly in 10% aqueous sodium thiosulfate than untreated silver halide crystals at a predetermined pH; characterized in that the silver halide crystals are made spontaneously developable in ordinary photographic developing solutions by a treatment with at least one amine borane compound.

In Example I, a quantitative test is disclosed which involves processing in the absence of any exposure to actinic radiation. The film is developed and then fixed, using times, temperatures, and solution compositions as fully described in that example. According to the prescribed test, the silver halide crystals suitable in the present invention should be spontaneously developable (i.e., developable without further treatment by radiation or by chemicals) to the extent that over 25% of the silver of said crystals remains as metallic silver after being processed according to the procedure described for Film Sample A."

In the above cited Blake application, Ser. No. 377,122, a somewhat more elaborate processing procedure is disclosed which also provides a useful means for defining silver halide crystals which are considered to be spontaneously developable.

In a practical embodiment of the invention, a gelatinosilver halide photographic emulsion is (a) photographically fogged by treatment with the amine borane compounds disclosed in assignees copending application, Bigelow and Burt, Ser. No. 392,625, filed Aug. 27, 1964, Patent 3,361,564, Jan. 2, 1968 and (b) treated with a solution of the organic compound to form a photosoluble silver halide layer. The preferred compounds are (1) heterocyclic amine boranes, and (2) alkyl amine boranes of the formula where R, is an alkyl radical of 1 to 20 carbon atoms and R and R are selected from the group consisting of hydrogen and an alkyl radical of 1 to about 20 carbon atoms. Suitable compounds include a, B, and 'y picoline borane, trimethylamine borane, morpholine borane, tertiary butylamine borane, dimethyl dodecylamine borane, and dimethyl octadecylamine borane. Certain of these amineboranes and other suitable amineboranes and methods of preparing such compounds are described in Inorganic Chemistry 3, 431-7 (1964), published by American Chemical Society.

The amine borane is employed in a concentration from about 10 to 1.0 gram per mole of silver halide, preferably from about 5 10 to 1X10 gram per mole of silver halide.

The fogged emulsion can be coated on a suitable support, and the coated emulsion bathed in a solution of an organic compound which forms a silver salt in intimate association with the silver halide crystals of the photographic emulsion. Particularly preferred organic compounds which form the desired silver salts (less soluble in water than the silver chloride) are the 2-mercapto-4- hydrocarbon thiazoles disclosed in assignees copending application of Blake, U.S. Patent No. 3,155,519, issued Nov. 3, 1964, especially 2-mercapto-4-phenylthiazole. In a more preferred manner, elements can be prepared by adding the organic compound to the fogged photographic emulsion prior to coating, as also disclosed in the above patent. In either event, the coated element comprises silver halide crystals in intimate association with the said silver salt of the organic compound.

The fogged element thus prepared is capable of forming a positive, photographic, silver halide image by imagewise exposure to actinic radiation followed by treatment with a silver halide solvent which removes silver halide more rapidly from the exposed than from the unexposed areas. It is then readily reduced to silver by an ordinary photographic developer with a fogging exposure step. Such a photographic developer may contain any of the usual photographic developing agents or combinations thereof, e.g., hydroquinone, p-methylaminophenol, p-phenylenediamine, pyrogallol, 3,4-diaminophenol-HC1, etc. The spectral sensitivity of the elements of this invention has been extended by the fogging action so that a positive image can be produced by exposure to longer wave length visible light.

The process of the present invention is not limited to a narrow class of organic compounds of photosoluble elements but may be employed with elements in which a wide variety have been used to insolubilize the silver halide crystals. The utility of a specific organic compound can be determined readily by relatively simple tests. Essentially the utility is determined by test A and test B as described in Fan, Ser. No. 403,632, filed Oct. 13, 1964. In test A, the candidate organic compound must render a dispersion of silver halide crystals insoluble in a silver halide solvent, e.g., an aqueous solution of sodium thiosulfate, at some pH between 1 and 13. The candidate compound must meet the insolubility requirements of test A, and also meet the requirements of test B by forming with said dispersion of silver halide crystals a reaction product which, upon treatment with an aqueous solution of sodium hypochlorite, becomes soluble when subsequently treated with aqueous sodium thiosulfate.

The silver halide dispersion disclosed in tests A and B above is a lithographic emulsion having a silver halide composition of 30 mole percent AgBr and 70 mole percent AgCl. The emulsion has 20 grams of gelatin present per mole of silver halide for the steps of precipitation and ripening and is freed of unwanted, soluble, byproduct salts by a coagulating and washing procedure as taught in U.S. Patent 2,489,341, wherein the silver halide and most of the gelatin are coagulated by an anionic wetting agent, sodium lauryl sulfate, using an acid coagulation environment. After washing, the emulsion coagulate is redispersed in water without additional bulking gelatin, maintaining a pH of 60:0.1 while stirring 10 min. at 110 F. Usually about 10 g. of gelatin is lost during washing, and the resulting emulsion, therefore, contains about 10 g. of gelatin per mole of silver halide.

The amount of the silver organic salt present in the photographic silver halide layer should be sufficient to protect the silver halide crystals, so that the unexposed crystals cannot be fixed by conventional fixing conditions, i.e., at normal times, temperatures and concentrations of silver halide solvents.

The gelatin/ silver halide ratio is quite flexible and may vary from about 7:1 to 1:20 depending on the particular organic compound and intended use for the emulsion layer. The imagewise solution of the exposed silver halide/ '4 organic compound stratum may be effected by the silver halide solvents commonly used as photographic fixing agents, e.g., sodium thiosulfate, alkali metal thiocyanate (e.g., sodium, potassium), concentrated solutions of potassium bromide, etc.

The desirable concentration of the organic compound which forms the required silver salt depends on many factors such as the solubility of the organic compound, the nature of its reaction with silver halide, the size and nature of the silver halide crystals, the presence of other materials which may react with or be absorbed to the surface of the silver halide, etc. Calculations given in Blake U.S. Patent No. 3,155,519 show that a useful concentration of the organic compounds is approximately that which can be theoretically determined as required to cover the silver halide surface with a so-called monomolecular layer. Also, elements suitable according to this invention can be prepared by bathing a photographic film in a solution of an appropriate organic compound. In this embodiment, the silver halide crystals near the surface of the coated emulsion stratum are in contact with a higher concentration of the organic compound. Crystals farther from the surface are treated with less of the organic compound and, if the rate of diffusion is sufficiently slow, there may be considerably less of the organic compound (even approaching zero) reacting with the lower than with the surface silver halide crystals. In such elements, satisfactory results might be obtained with only a fraction, e.g., one-half, of the amount of the organic compound theoretically calculated as required to just cover the surface of a mole of the silver halide crystals.

With regard to tests A and B, it can be determined readily that the organic compound should be present in such an amount, in terms of the ratio of its weight to the surface area of said silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide (/30 mole per cent) gelatin emulsion containing 10 g. of gelatin per mole of Ag and 0.57 mg. of Ag/mL, and said silver chlorobromide dispersion is treated with 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver and mg. of sodium thiosulfate), at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively treated with 5%, by weight, aqueous sodium hypochlorite and 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver, 25 mg. of sodium hypochlorite and 100 mg. of sodium thiosulfate), after vigorous agitation of the dispersions for 30 seconds at 25 C.

In a preferred embodiment of the invention prefogging and organic compound treatment of the silver halide is such that the resulting photosoluble element cannot be exposed and developed conventionally to a practical negative silver image due to high fog.

Useful photosoluble elements for this invention may contain optical sensitizing dyes and the processing of the elements may be improved by the use of an inorganic cation (e.g., K+, Rb' Cs+, Pb etc.) in the silver halide solvent solution disclosed, respectively, in assignees copending applications of Blake, Ser. No. 390,460, filed Aug. 18, 1964, Patent 3,384,485, May 21, 1968, and Hunt, Ser. No. 388,919, filed Aug. 11, 1964.

The invention will be further illustrated by but is not intended to be limited to the following examples wherein red safelights (or total darkness) were used throughout the preparation, coating and drying of the emulsions and throughout the processing of the elements:

EXAMPLE I A light sensitive gelatino-silver chloride coagulate, made by precipitation and coagulation washing in the manner taught in Moede, U.S. 2,772,165, was redispersed in gelatin so as to achieve a gelatin to silver halide weight ratio of 1 to 2.8. The resulting emulsion was digested in the presence of 0.01 gram of morpholine boran per mole of silver chloride at 130 F. for 20 minutes, and later digested for 20 minutes at 160 F. in the presence of 0.75 gram of 2-mercapto-4-phenylthiazole (hereinafter designated as MPT) per mole of silver chloride. A chrome alum hardening agent was added to the emulsion which was then coated on a vinylidene chloride copolymer subbed polyester base prepared as described in Example IV of Alles U.S. Patent 2,779,684 (and to which a gelatin sub layer had been subsequently applied). The coating weight, in terms of metallic silver content, was determined by means of X-ray fluorescence to be 53 mg./dm. The dried element was exposed sensitometrically through a standard /2 step Wedge to a high intensity tungsten filament lamp (a DXC floodlamp) at 26" for seconds. Following this, the exposed sample was processed for 40 seconds at 68 F. in a conventional acid photographic fixer, washed with tap water for 30 seconds and placed for one minute at 68 F. in a photographic developer. Compositions of the fixer and developer are as follows: Acid fixer composition H2O ml Na2S203 g Na SO (anhyd) N32B407' Glacial acetic acid ml KAI (SO -l2H O g H O to 1000 ml. pH, about 4.5.

Developer composition H O ml Na SO (anhyd.) ....g Hydroquinone 1-phenyl-4-methyl-3-pyraz0lidone Boric acid g KBr g S-nitrobenzimidazole nitrate (solution of 1 g. in 100 ml. EtOH) ml 1-phenyl-5-mercaptotetraz0le (solution of 1 g. in

100 ml. EtOH) -Inl NaOH g H O to 1000 ml.

The film was given a final water wash and dried in air. The positive white silver halide image, the formation of which occurred during the fxing step, was intensified during the subsequent treatment with the photographic developer solution. Thus the silver halide image was converted by reduction to a black, metallic silver, positive image. It is to be noted that the customary white light flashing prior to development was not required since the element was made spontaneously developable during manufacture by the treatment with morpholine borane.

Two other samples of the above film were processed at 68 F. in the absence of any exposure to light. Sample A alone was treated for one minute in the above photographic developer but both film sample A and film sample B were treated in the above fixing solution for ten minutes. A control film, which was manufactured without the fogging treatment with morpholine borane, was proccessed like film sample A, i.e., developed and fixed. Silver coating weights were determined by X-ray fluorescence before and after processing, the results being tabulated below:

AMINE BORANE PRE-FOGGED FILM Untogged Film film (no sample amine Develop B borane) Develop (min.) Fix (m1n.) 10 Ag coating weight (before processing) A '"-'tra 51 g coa mg weig a or processing 1 g. (1111. 10

In the present application the term spontaneously developable is used to describe silver halide crystals which are developable (without further fogging treatment by radiation or by chemicals) to the extent that over 25% of the silver of the crystals remain after the processing above for film sample A. In this case, the fraction of remaining silver in film sample A was 44/53, or 83%.

EXAMPLE II A light sensitive gelatino-silver chlorobromide coagulate (containing 30 mole percent of AgBr and 70 mole percent AgCl) was made by precipitating and coagulation washing in the manner taught in U.S. Patent 2,489,- 341, wherein the silver halide and most of the gelatin were coagulated by an anionic wetting agent, sodium lauryl sulfate, using an acid coagulation environment. This coagulate was redispersed in gelatin to form an emulsion which was then treated in the manner described in Example I, except that only .50 gram of MPT was used to insolublize a mole of silver halide.

The resulting film was also spontaneously developable as a photosoluble film. Thus the processing sequence described in Example I gave a satisfactory direct positive image without the need for a fogging exposure.

EXAMPLE III A gelatino-silver chloride emulsion was precipitated, washed, and redispersed as described in Example I. This emulsion was then treated in the manner described in Example I except that 0.02 g. of tertiary butylamine borane was used in place of the morpholine borane of that example.

This also resulted in a spontaneously developable photo soluble film. Thus the processing sequence described in Example I gave a satisfactory direct positive image without the need for a fogging exposure.

EXAMPLE IV A gelatino-silver chloride emulsion was precipitated, washed, redispersed and further treated in the manner described in Example I except that 0.02 g. of trimethylamine borane, 0.6 g. of dimethyl dodecylamine borane and 0.6 g. of dimethyl octadecylamine borane were used in respective portions of the emulsion instead of the morpholine borane of Example I. These substitutions resulted in spontaneously developable photosoluble films which, by the processing sequence described in Example I, gave satisfactory direct positive images without the need for a fogging exposure.

EXAMPLE V A gelatino-silver chloride emulsion was precipitated, washed, redispersed and further treated in the manner described in Example I except that 2-mercapto-4,5-diphenyl oxazole was used in place of the MPT of Example I.

This also resulted in a spontaneously developable photosoluble film which, by the processing sequence described in Example I, gave a satisfactory direct positive image without the need for a fogging exposure.

Suitable organic compounds which may be used to form silver salts in intimate association with the silver halide crystals are those disclosed in various patents of the assignee, i.e., Blake, U.S. Patents 3,155,507; 3,155,514; 3,155,516 through 3,155,519 and Celeste and Cohen U.S. Patent No. 3,155,515. Other suitable organic compounds are disclosed in various copending applications of the assignee, i.e., Fan, U.S. Ser. No. 403,631, Patent 3,284,206, Nov. 8, 1966, and 403,632, Blake, U.S. Ser. No. 403,661 and Blake and Fan, U.S. Ser. No. 403,660, all filed Oct. 13, 1964, Patent 3,368,899, Feb. 13, 1968.

In place of part of the gelatin of the silver halide emulsion, other natural or synthetic water-permeable organic colloid binding agents can be used. In some cases such binders can be used alone. Such agents include water-permeable or water-soluble polyvinyl alcohol and its derivatives, e.g., partially hydrolyzed polyvinyl acetates, polyvinyl ethers and acetals containing a large number of intralinear -CH -CHOH- groups, hydrolyzed interpolymers of vinyl acetate and unsaturated addition polymerizable compounds such as maleic anhydride, acrylic and methacrylic acid esters and styrene. Suitable compounds of the last-mentioned type were disclosed in US. Patents 2,276,322; 2,276,323 and 2,397,866. The useful polyvinyl acetals include polyvinyl acetaldehyde acetal, polyvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal. Other useful colloid binding agents include the poly-N-vinyl lactams of Bolton US. Patent 2,495,918 various polysaccharides, e.g., dextran, dextrin, etc., the hydrophilic copolymers in Shacklett, US. Patent 2,833,650, hydrophilic cellulose ethers and esters, and polymers of acrylic and methacrylic esters and amides.

The emulsion may optionally contain any of the usual adjuvants customarily employed in silver halide systems as long as they do not interfere with the insolubilizing action of the silver salt of the organic compound or the prefogging action of the amine borane compound of this invention.

The emulsions can be coated on any suitable support e.g., films of cellulose esters, cellulose mixed esters; superpolymers, e.g., poly(vinyl chloride co vinyl acetate), polyvinyl acetals, butyrals; polystyrene; polyamides, e.g., polyhexamethylene adipamide, polyesters, e.g., polycarbonates, polyethylene terephthalate, polyethylene terephthalate/isophthalate, esters formed by condensing terephthalic acid and its derivatives, e.g., dimethyl terephthalate with propylene glycol, diethylene glycol, tetramethylene glycol, cyclohexane-1,4-dimethanol (hexanhydro-p-xylene dialcohol); paper, metal, glass, etc.

An important advantage of the novel elements of this invention is that the silver halide positive image can be intensified to a metallic silver image, easily and conveniently. The prefogging which makes this possible can be carried out during manufacture of the film, thus significantly simplifying the work of processing by eliminating a previously required step. The elimination of a postflashing exposure is a particular advantage when processing in a darkroom containing other photographic elements which could suffer damage from the flashing.

The particular advantage of prefogging with the preferred amine borane compounds of this invention is the reproducibility of the operation. Although various other chemical fogging agents have been used, none has given results as dependable as the amine boranes. Another advantage of this invention is the extension of the emulsions spectral sensitivity to longer wavelengths.

This invention is concerned with intensification of the positive silver halide image obtained after treatment with a silver halide solvent, especially the intensification obtained by reduction of the silver halide to a metallic silver image in the absence of any postflashing exposure. However, it should be noted that the originally formed positive silver halide image may, with or without a waterwashing step, be dried and used without further treatment, e.g., for viewing by projection, with no harmful effects caused by the presence of the amine borane prefogging agent. Furthermore, the amine borane compound will not interfere with alternate methods of intensifying the silver halide image, e.g., by toning it with sodium sulfide, sodium selenide, etc., or by converting it to a dye image, e.g., by reacting it with a primary aromatic amine color developing agent in the presence of a color coupling compound either in the developing bath or previously present in the emulsion.

I claim:

1. A photo'soluble smulsion layer comprising before imagewise exposure to actinic radiation, a. dispersion of light-sensitive silver halide crystals having intimately associated therewith a silver salt of an organic compound of lower solubility in water than silver chloride, said associated silver halide crystals dissolving more slowly in 10% aqueous sodium thiosulfate than untreated silver halide crystals at a predetermined pH; characterized in that the silver halide crystals are made spontaneously developable in ordinary photographic sliver halide developing solution by treatment with at least one amine borane compound to the extent that over 25% by weight of the silver of said crystals remains as reduced silver after development for one minute in an aqueous developer of the following composition:

H O ml 800 Na SO (anhyd) g Hydroquinone g 16 1-phenyl-4-methyl-3-pyrazolidone g 1 Boric acid -g 5.5 KBr g 2 S-nitrobenzimidazole nitrate (solution of 1 g. in

ml. EtOH) ml 40 1-phenyl-S-mercaptotetrazole (solution of 1 g. in

100 ml. EtOH) ml 10 NaOH g 24 H O to 1000 ml.

2. A layer according to claim 1 wherein said silver salt is a mercaptide and said organic compound is an organic mercaptan.

3. A layer according to claim 1 wherein said silver salt is a mercaptide and said organic compound is an organic mercaptan of the formula where R is a hydrocarbon nucleus of 420 carbon atoms.

4. A layer according to claim 1. wherein any metal salt present has an atomic weight as great as silver.

5. A layer according to claim 1 containing silver chloride crystals dispsersed in gelatin.

6. A layer according to claim 1 treated with an alkylamine borane of the formula where R, is alkyl of 1 to 20 carbon atoms and R and R are each hydrogen or an alkyl radical of 1 to 20 carbon atoms, in an amount from 10* to 1.0 gram of said borane per mole of silver halide.

7. A layer according to claim 1 treated with trimethylamine borane in an amount from 10- to 1.0 gram per mole of silver halide.

8. A layer according to claim 1 treated with t-butylamineborane in an amount from 10" to 1.0 grams per mole of silver halide.

9. A layer according to claim 1 treated with morpholine borane in an amount from 10* to 1.0 gram per mole of silver halide.

10. A layer according to claim 1 wherein the associated organic compound is present in such an amount in terms of the ratio of its weight to the surface area of said silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide (70/30 mole percent) gelatin emulsion containing 10 g. of gelatin per mole Ag and .57 mg. of Ag per ml., and said silver chlo- 9 10 robromide dispersion is treated with 10%, by Weight, References Cited aqueous sodium thiosulfate (so that the resulting mixture UNITED STATES P N S contains mg. of Silver and Of sodium thiO- Hillson sulfate), at least three times the amount of silver ohloro- 155 5 9 1 /1964 Blake 95 1 7 bromide remains undissolved as compared with a similar 5 3,361,564 1/1963 Bi l et 96 ..64

dispersion successively treated With 5%, by Weight,

aqueous sodium thiosulfate (so that the resulting mix- NORMAN TORCHIN, Primary Examinerture contains 0.29 mg. of silver, 25 mg. of sodium hy-- I, R, EVERETT, Assistant Examiner. pochlon'te and 100 mg. of sodium thiosulfate), after 10 vigorous and essentially equal agitation of both dispersions for 30 seconds at 25 0. 109 

